In general, a substrate processing apparatus for performing an etching process on a substrate, e.g., a semiconductor wafer (hereinafter, referred to as a ‘wafer’), has an accommodation vessel (hereinafter, referred to as a ‘chamber’) for accommodating the wafer therein. In such a substrate processing apparatus, a high frequency power is applied into the chamber to produce a plasma from a processing gas such as a CF4 based gas or the like, and an etching process is carried out on a surface of the wafer by using a produced plasma.
In the chamber, there are disposed various parts for maintaining the plasma at a predetermined state; and a focus ring has been known as one of these. The focus ring is a ring-shaped part and is disposed to surround a periphery of a circular plate-shaped wafer in the chamber. The focus ring needs to have a similar electric characteristic, e.g., conductivity, to that of the wafer to guide the plasma in the chamber to the wafer efficiently. Thus, a conventional focus ring has been formed by silicon (Si).
Since, however, the silicon is eroded by the plasma, the focus ring is consumed and deformed in the chamber in a short period. If the focus ring is deformed, the plasma state on the wafer is changed. Thus, the focus ring needs to be replaced in a short period in case where a silicon focus ring is employed.
Therefore, a focus ring made of silicon carbide (SiC), which is known as a material that is hardly eroded by the plasma, has been used recently. Silicon carbide has substantially the same conductivity as the wafer; and it does not incur metal contamination under a plasma atmosphere. Therefore, it is advantageously employed as a part in the chamber.
As for the silicon carbide, there have been known a sintered silicon carbide formed by a sintering method and a CVD silicon carbide formed by a CVD method. The amounts of wear of the former and the latter due to the plasma are about 15% less and about 50% less, respectively, compared to that of silicon.
Since, however, the sintered silicon carbide is known to be likely to produce particles, it has been proposed that a surface of the focus ring formed by the sintered silicon carbide is coated with the CVD silicon carbide that is unlikely to produce particles (see, e.g., Japanese Patent Laid-open Application No. 10-135093). Hence, it is possible to suppress particle generation from the focus ring.
However, the CVD silicon carbide is obtained by introducing a material gas around a graphite base material disposed in a high temperature atmosphere, to form a silicon carbide thick film on a surface thereof; and cutting off a formed thick film. Further, since a surface of the CVD silicon carbide thus obtained is rough, lapping is carried out on the focus ring to improve the appearance and to prevent particle scattering by smoothing the surface thereof. Hence, the manufacture of the focus ring by using the CVD silicon carbide is rather difficult.
Further, even though the CVD silicon carbide is unlikely to produce particles, some particles are still produced. In particular, many particles are generated during an initial etching process after a loading a new focus ring, specifically, for initial 120 hours of a high frequency power application. Accordingly, in case where the CVD silicon carbide focus ring is employed, a seasoning process needs to be performed for a long period to stabilize an atmosphere in the chamber after the exchange of the focus ring; hence a decrease in an operating rate of the substrate processing apparatus becomes problematic.